P-Channel MOSFET Load Switch w/ Soft-Start

How soft? How fast?

John

Soft-start ON rise time would be nice to have it be a few milliseconds, or adjustable by a 1206 capacitor. As for switch-OFF time, I don't really have an answer. From reading datasheets of other MOSFET drivers, I have seen fast OFF times as being a feature of the drivers, so I assumed that meant fast OFF switching time was good thing to have. This design will be for a generic battery pack controller board that will potentially be powering several different types of electronic loads. An example of a part I'm looking for would be similar to the Fairchild Semi FDG901D. This part would be perfect but it only works to 6V.

P Channel FETs in the supply are controller by an NPN on the GND. Meaning have a pullup on the gate of 20k or so, and have an NPN with an emitter resistor on GND forming a current sink. The base can be connected to the logic.

Choose the emitter resistor such that sufficient current flows while the voltage on the gate doesn't exceed 10V or so.

Speed is an issue for the resistor values.

Rene

What is the advantage of using an NPN as the P MOSFET controller instead of using a small signal logic-level N MOSFET to control it??

You could did that too!